APSTUD-8264 After upgrade to 3.6 switching workspaces requires forcequit

under debugger it looks like AptanaDB/Derby cause this. Derby is overkill for what we're doing here, so I'm going to clean up the code to persist analytics events to disk, and remove Derby altogether.

All the methods are synchronized, meaning that every call blocks until any previous call is done. So we shouldn't be able to call clear on an event before the event is fully written.